Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. Left-over products of the combustion are exhausted out of the turbine and may provide thrust in some applications. As a result, very high working temperatures are experienced by the turbine.
Design of gas turbine engines is driven by many concerns, however, maximizing engine efficiency to minimize costs of operation and environmental impact due to emissions are becoming increasingly important. Gas turbine efficiency is maximized by increasing a maximum operating temperature of the gas turbine engine. As a result, efficiency is limited by the temperature capabilities hot components such as turbine blades, turbine vanes, turbine blade tracks, combustor liners, etc.
Temperature capabilities of hot components may be increased through cooling, materials, and coatings of the components. Some materials, such as nickel-based (Nibased) superalloys have reached an intrinsic limit in high-temperature resistance. As a result, development has focused on Thermal Barrier Coatings (TBC), which may be brittle, and Ceramic Matrix Composite (CMC) materials, which sometimes suffer from load transfer problems.
CMC materials include various components which may include Silicon and Carbide. In one example, SiC/SiC CMC materials may be used in hot section structural components for generation gas turbine engines. SiC/SiC CMC engine components provide desirable high-temperature mechanical properties, high-temperature physical properties, and chemical properties. These desirable properties allow gas turbine engines to operate at relatively higher temperatures than the current engines having superalloy components. SiC/SiC CMC materials also provide the additional benefit of damage tolerance, which monolithic ceramic materials do not possess.
However, combining CMC materials with metal materials has some issues. One issue is that CMC materials often have a different stiffness than metal components in which the CMC materials may be joined to. Another issue is that CMC materials have different Coefficients of Thermal Expansion (CTE) than metal materials they may be joined to. As a result, significant stresses may be result where CMC materials are joined to non-CMC materials.